This invention relates to a quiet cooling system for internal combustion engines which includes a radial fan and a ring radiator, the radiator being mounted at the circumference of a radial impeller at a distance from the latter. The invention relates, more particularly, to such a system in which the radiator is made integral or of radiator segments, the radiator including tubes conducting water, cooling fins being fastened to the tubes.
By the mid 1980's, the permissible noise level of motor vehicles equipped with internal combustion engines will be approximately 10 dB(A) below the values currently permitted. In addition to reducing noise emitted by the internal combustion engine and its components, the noise level produced by the cooling system associated with the internal combustion engine will also have to be decreased approximately 10 dB(A).
Numerous proposals have been made in attempts to achieve the noise reduction goal. The proposals, in most cases, provide for increasing the front surface of conventional, flat radiators. This is intended to result in a corresponding reduction of the pressure loss, so that circumferential velocity of the fan, which is especially critical for noise production, can be reduced.
Such cooling systems, however, require so much space that they cannot be accommodated in the engine compartments of motor vehicles. For this reason, some proposals provide for installation behind the cab of a vehicle or on the cab roof of the vehicle. Both designs have considerable disadvantages, namely, shortening of the truck floor and/or an unfavorable load on the cab, as well as an increase danger of scalding in the event of accidents.
Cooling systems with ring radiators and radial fans are also known. However, known designs suffer from numerous disadvantages.
Usually, radiators with radially disposed ribs are used, the ribs being aligned with circularly bent cooling tubes. This results in a considerable loss of thrust for the air, since the cooling air enters the radiator with a large circumferential component.
To avoid these thrust losses, several known designs bend the cooling ribs in such manner that their entrance angle corresponds to the influx angle, such as the respective radiators disclosed in British Pat. No. 153,175; and in German Federal Republic Pat. No. 1,576,705. Manufacturing cooling ribs shaped in this fashion, however, increases the cost of the radiator. It is also difficult to achieve the correct entrance angle, so that considerable thrust losses can still develop. Moreover, the influx angle of the cooling air varies with the operating state of the vehicle, so that a smooth design can be achieved only for a specific operating point, depending on the vehicle speed and/or the exit angle. In other known ring radiators, disk-shaped plates are used to guide the water using cooling ribs disposed between the plates and so as to be radial or inclined in the direction of the incoming flow of cooling air, such as disclosed in German Federal Republic Auslegeschrift (Published Patent Application) No. 1,551,519 and German Federal Republic Offenlegungsschrift (Laid Open Patent Application) No. 1,925,809.
However, the manufacture of these designs is still costly and radiators so constructed still suffer from high, undesirable thrust losses.
Ring radiators built up of segments are also known as rotating heat exchangers, whose tubes run parallel to the axis of rotation. In this manner, the rotating heat exchanger itself acts as a fan, for example, as disclosed in German Federal Republic Offenlegungsschrift (Laid Open Patent Application) No. 2,610,673.
In order to maintain the necessary cooling area, the radiator width of known systems is usually greater than the exit width of the radial fan (German Auslegeschrift No. 1,551,519, Supra; German Pat. No. 1,576,705, supra). In order to achieve an air distribution which is as uniform as possible over the entire width of the radiator, conical guide rings are disposed side by side between the fan and radiator, so that a plurality of diffusing rings forms a cross section which increases gradually from the impeller outlet width to the width of the radiator, for example, as disclosed in German Federal Republic Offenlegungsschrift (Laid Open Patent Application) No. 2,050,265. This measure also increases manufacturing costs, and results in an increase in the diameter of the cooling system.